My first kyusu ever arrived in the mail today from Hojo. I am so pleased! No more using a sink strainer for sencha or fuka-like leaves . Artist is Gyokko and it is made from red clay using the Yohen technique. You can't tell from my photo (I will master that later) but it is black with rusty red on the spout and handle fading into the surrounding black. It brewed up a heavenly batch of Hon Yama Hebizuka for me, which Hojo included as a sample. I will be reviewing that one as it is scrumptous.

Great job, Rebecca. I need a Gyokku ... I quite like his work. Also nice Seigan Guinomi!

The Gyokku I believe is reduction fired (a Japanese guy told me it was deox fired, absence of oxygen) which causes the change to black from reddish clay. Often part of a Gyokku still shows the red which is due to positioning in the kiln.

Yohen is an interesting term ... it could be one of those words that have multiple meanings in firing techniques. The Bizen I pictured earlier is Yohen, which I think is translated to "changed by the fire." Perhaps one of our artisans will pop in and clarify this.

But most Yohen pieces I see have some degree of knarlyness and were wood fired. The two on the right are Yohen ... as I understood it.

During my email conversations with Akira from Hojo's, he told me that this Gyokko was created using the Yohen technique. I would surely like to know if it is not, simply so I might be correct in my description of the piece...which the description came directly from Akira. I'll check out the artisan forum.

I found some interesting explanations of the term "Yohen" in the context of Japanese pottery. When I went to actual artisan's websites and also checked the meaning of the term in historical context, this site provided an interesting explanation of the term's meaning: http://www.2000cranes.com/Kosei-Tamaya.htm It will be interesting to hear from the experts!

rjiwrth wrote:During my email conversations with Akira from Hojo's, he told me that this Gyokko was created using the Yohen technique. I would surely like to know if it is not, simply so I might be correct in my description of the piece...which the description came directly from Akira. I'll check out the artisan forum.

It is difficult to see the surface of the Gyokku kyusu. On the Artistic Nippon site, he shows Yohen kyusu by Gyokku so the artist incorporates this into his work. But Yohen has usually a more random effect as seen on Chip's Bizen yaki. I wonder if it is controllable?

Also, reduction firing, as I am told, doesn't produce a black teapot but a purpleish-gray color as we see in Banko kyusu. Hibiki-an sells a Tokoname kyusu which is black in color and on the very edges, one can see the red clay. They describe it as follows: "The surface of Tokoname Yaki are generally vermilion or black in color. The vermilion color is due to iron that is contained in the local soil. The black color is created by placing carbon on the surface of the Kyusu. When this is heated to a high temperature, the iron and carbon create a black color."

In reduction firing, nothing is added to acheive the purplish-gray color. It is a natural process turning the red clay into this color. It actually changes the iron structure of the clay from Fe3 to Fe2, hence, reduction.

I've searched and it looks like colors achieved by yohen are endless, at least from what I have discovered. Still waiting for expert artisans to comment. This is a close-up of a Gyokko pot on Artistic Nippon website that is actually the brother to my current pot. You can easily see the texture and is a replica of mine's surface and coloration. My photo didn't capture squat I had my choice between the one I purchased and also the one below:

As I understand to term "Yohen" (only from books and from talking with mister Kusakabe-I can not speak Japanese) It means touch of fire. And on the pot you put link to I can not see this effect, this touch. Sometimes effect of fire is very soft (because of position in the kiln for example) and unobtrusive so it is hard to say it from pictures for sure but from my experiences it is not Yohen.

As I understand to term "Yohen" (only from books and from talking with mister Kusakabe-I can not speak Japanese) It means touch of fire. And on the pot you put link to I can not see this effect, this touch. Sometimes effect of fire is very soft (because of position in the kiln for example) and unobtrusive so it is hard to say it from pictures for sure but from my experiences it is not Yohen.

This is exactly what I was told when I inquired from the seller what kind of clay it is made from: "Gyokko 02 kyusu is made of one kinds of red clay. It appears reddish color because of reduction baking method.It appears dark blue on one side and reddish brown at another side. 2 tones were made by the technique called Yohen". For clarification, I got my pot from Hojo, not from Artistic Nippon. Artistic Nippon's site is just more explanatory so that's why I used that link. Its nearly the same pot except for shape.

Chip wrote:This is something I never really knew ... and did not know I did not know. Thanks for the enlightenment, Petr. Thank you for posting Tead Off.

I seriously think there is no one correct answer in Reduction versus Yohen.

Reduction is the deprivation of oxygen at a certain point in the firing. This changes the color of the clay or glazing. Reduction is possible in all kilns, I think.

Yohen, if I am correct, is something that happens to the surface during a wood firing, where the fire changes the color and adds effects. I don't think you can get Yohen from gas or electric kilns. I'm not an expert.

There is now a lot of info down in the Teaware Artisans Q+A thread getting into this youhen stuff, if anyone is interested in the details.

As to "reduction"........ it is actually a chemists term. In this context it basically means to remove oxygen from a compound. In ceramics the main reducing agents are carbon monoxide gas and to a lesser degree hydrogen gas. To get these gasses inside the kiln the combustion reactions are starved of adequate oxyegn to go to completion ........ so instead of full combustion you get partial combustion. The end byproducts of that incomplete combustion are carbon monoxide and hydrogen. However this is not a direct route... and so there are all manner of intermediary partial combustion compounds created including stuff like aldehydes and so on....as the fuel molecules "crack" and tries to burn. Complex process.

Although there are others, the most usual compound involved in this reduction / youhen endeavor in pottery is Fe2O3. At elevated temperatures the affinity that CO (carbon monoxide gas) has for the Oxygen atoms in red iron oxide is greater than the bonds that hold that Oxygen into the iron oxide molecule. So the Oxygen is removed from the Fe2O3, "reducing" it to a lower state ....as in FeO. FeO is the black form of iron oxide.

The "magic" in this is that in the FeO state, black iron oxide not only imparts blackish coloring properties but it also is a very powerful flux acting upon silica ( SiO2 ) the prime glass former in ceramics, and material that is present in all claybodies (and almost all glazes). This fluxing action makes clay bodies containing lots of red iron oxide more dense (viterous... melted) when reduced and the red iron oxide is cinverted to the black form. It also colors the forming glassy matrix that is gluing the crystalline parts of the clay body together. Various combinations of red iton oxide and black iron ocide forming inside and on the surface of the claybody help to cause a lot of the youhen effects.

The purple-ish shades of some clay are caused by a mixture of the various states of iron oxide that are possible.... which can include some fraction of even fully reduced iron oxide...... elemental iron.

The exact timing of the oxygen starved firing conditions is important, as is the amount of CO versus H2. Hydrogen is a much smaller sized molecule when compared to carbon monoxide. So it is able to penetrate into pores in claybodies and fusing glazes that CO cannnot. I could write a book on this stuff... we are just scratching the surface.

Yes, this is true. Pretty much any fuel fired kiln can do this easily. Electric kilns are a little trickier... but it can be done there too. However creating reduction in an electric kiln takes its toll on the electrical elements. And you have to get a fuel source in there somehow.

Many potters (here in the USA) think this is not really possible with electric kilns.....but it is. In Japan some of the most gorgeous work I have seen out of some people I know there like Miura-sensei at Geidai and Kondo-sensei in Kyoto ...that you would swear was fired in a fuel burning kiln..... is fired in electric kilns with tiny wood fireboxes on them to create reduction (not heat) at the correct times.

The replacement of electrical elements every so often is just the "cost of doing business" if you want to fire reduction in an electric kiln. (There are some tricks to protect the elements a bit too.)

By the way...... my acquantience Kondo-san was telling me two years ago that in Kyoto now it is impossible to fire even new reduction kilns. His recently independent apprentice had to move out of the city when he set out to start his pottery and wanted a gas kiln. Kondo-san said their electric reduction kiln is still allowed due to the heavy family status/history in Kyoto (Kondo Uzo - Living National Treasure in porcelain). Wood kiln firing in Kyoto has been restricted ever since I have been going to Japan....years and years.... due to air pollution restrictions. Kyoto sort of sits in a valley with mountains (hills really) surrounding it and creating a great environment to trap air pollution. (Sort of like Salt Lake City in the USA.)

Tead Off wrote:Yohen, if I am correct, is something that happens to the surface during a wood firing, where the fire changes the color and adds effects. I don't think you can get Yohen from gas or electric kilns.

Youhen is not necessarily totally restricted to wood firing........ although that is the most common source of such effects. There are many types of fire change effects that are done in Japan in gas and even electric kilns. Most ware in Japan is fired in gas and electric kilns these days. The wood kiln in Japan is an expensive luxury beast. They require a decent amount of land. Land is expensive in Japan. Wood is typically VERY expensive in most parts of Japan. There is a blight that is infecting the aka matsu (Japanese red pine) in the southern part of Japan.....making that wood (the PRIME choice for firing noborigama) rather scarse and expensive. And traditional types of wood kilns produce a goodly amount of smoke...... so as population grows... the locations that wood kilns can continue to fire are getting more and more restricted.